Mechanical and chemical-mechanical planarization and polishing processes (collectively “CMP”) remove material from the surfaces of microfeature workpieces in the production of microelectronic devices and other products. FIG. 1A schematically illustrates a rotary CMP machine 10 having a platen 22, a polishing pad 20 on the platen 22, and a carrier 30 adjacent to the polishing pad 20. The CMP machine 10 may also have an under-pad 23 between an upper surface 21 of the platen 22 and a lower surface of the polishing pad 20. A platen drive assembly 24 rotates the platen 22 (as indicated by arrow A) and/or reciprocates the platen 22 back and forth (as indicated by arrow B). Because the polishing pad 20 is attached to the under-pad 23, the polishing pad 20 moves with the platen 22 during planarization.
The carrier 30 has a carrier head 31 with a lower surface 33 to which a microfeature workpiece 12 may be attached, or the workpiece 12 may be attached to a resilient pad 32 under the lower surface 33. The carrier head 31 may be a weighted, free-floating wafer carrier, or a carrier actuator assembly 34 may be attached to the carrier head 31 to impart rotational motion to the microfeature workpiece 12 (as indicated by arrow C) and/or reciprocate the workpiece 12 back and forth (as indicated by arrow D).
The polishing pad 20 and a polishing solution 50 define a polishing medium 51 that mechanically and/or chemically-mechanically removes material from the surface of the microfeature workpiece 12. The polishing solution 50 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the microfeature workpiece 12, or the polishing solution 50 may be a “clean” nonabrasive planarizing solution without abrasive particles. In most CMP applications, abrasive slurries with abrasive particles are used on nonabrasive polishing pads, and clean nonabrasive solutions without abrasive particles are used on fixed-abrasive polishing pads. Abrasive slurries can include suspensions of fumed or colloidal abrasive ceramics such as silica, ceria or alumina, or suspensions of particles that are formed from a composite of colloidal silica and a polymer. Such slurries are available from JSR Micro of Sunnyvale, Calif.
To planarize the microfeature workpiece 12 with the CMP machine 10, the carrier head 31 presses the workpiece 12 face-down against the polishing pad 20. More specifically, the carrier head 31 generally presses the microfeature workpiece 12 against the polishing solution 50 on a polishing surface 25 of the polishing pad 20, and the platen 22 and/or the carrier head 31 move to rub the workpiece 12 against the polishing surface 25. As the microfeature workpiece 12 rubs against the polishing surface 25, the polishing medium 51 removes material from the face of the workpiece 12.
The CMP process must consistently and accurately produce a uniformly planar surface on the microfeature workpiece 12 to enable precise fabrication of circuits and photo-patterns. One problem with existing CMP methods is that the polishing surface 25 of the polishing pad 20 can wear unevenly or become glazed with accumulations of polishing solution 50 and/or material removed from the microfeature workpiece 12 and/or the polishing pad 20. To restore the planarizing/polishing characteristics of the polishing pad 20, the pad 20 is typically conditioned by removing the accumulations of waste matter with a conditioner 40. Such conditioners and conditioner assemblies are available on most CMP polishing tools, such as those manufactured by Applied Materials of Santa Clara, Calif. under the trade name Mirra.
The existing conditioner 40 typically includes an abrasive end effector 41 having a head 45 generally embedded with diamond abrasives. The head 45 is attached to a shaft 42 which connects to a shaft housing 49. The shaft housing 49 is supported relative to the polishing pad 20 by an arm 43 and a support housing 44. A motor 46 within the support housing 44 rotates the shaft housing 49, the shaft 42 and the head 45 (as indicated by arrow E) via a pair of pulleys 47a, 47b and a connecting belt 48. The conditioner 40 can also include a separate actuator (not shown in FIG. 1A) that sweeps the arm 43 and the end effector 41 back and forth (as indicated by arrow F). A bladder 39 rotates with the shaft 42 and applies a normal force to the head 45 (as indicated by arrow G) to press the head 45 against the polishing pad 20. The end effector 41 accordingly removes a thin layer of the polishing pad material in addition to the waste matter to form a new, clean polishing surface 25 on the polishing pad 20.
One drawback with the foregoing arrangement described above with reference to FIG. 1A is that the end effector 41 may not be suitable for conditioning a fixed abrasive polishing pad. For example, the end effector 41 can tear the material forming the polishing pad 20, reducing the uniformity of the polishing surface 25, and therefore reducing the uniformity with which the polishing pad 20 removes material from subsequent workpieces. Conventional slurries, which include a suspension of ceramic particles, tend to have the same effect on a fixed abrasive polishing pad.
One approach to addressing the foregoing drawback is to brush the polishing pad 20, either after the conditioning process or instead of the conditioning process. FIG. 1B illustrates a brush 38 having bristles 37 that pass over the polishing surface 25 of the polishing pad 20. Accordingly, the bristles 37 clean the exposed surfaces of fixed abrasive elements 26 embedded in projections 19 of the polishing pad 20. One drawback with this arrangement is that it has only a limited beneficial effect on the polishing rate of the polishing pad 20. One possible explanation for this result is that the bristles 37 are relatively large in comparison to the abrasive elements 26 and the contact between the bristles 37 and the abrasive elements 26 is not uniform. Another possible explanation is that the bristles 37 can extend into the gaps 18 between adjacent projections 19 in which the abrasive elements 26 are housed. Accordingly, the bristles 37 can loosen deposits and/or pad material in these regions, which can cause scratching or other defects in workpieces that are subsequently processed with the polishing pad 20.